The present invention relates to a propylenic copolymer and its film. More precisely, the invention relates to a binary random copolymer of propylene and ethylene, and to a film to be formed by sheeting the copolymer. As having an excellent low-temperature heat-sealing property, the copolymer and its film are favorably used as sealant layers of laminate films to be produced through lamination or co-extrusion. The invention also relates to a multi-layered film as produced by laminating or co-extruding a sealant layer of the propylenic random copolymer on at least one surface of a propylenic random copolymer substrate with good stiffness.
As having good stiffness, transparency and moisture resistance, films such as biaxially-stretched films or T die-cast films of crystalline propylene polymers are widely used as wrapping films. Wrapping films are generally formed into bags through heat sealing, and the bags are closed also through heat sealing after having been charged with contents. Therefore, for such wrapping films, preferred are multi-layered films having a sealant layer of a resin with good heat-sealability at low-temperature on their one or both surfaces, to films of propylene homopolymers with poor heat-sealability at low-temperature.
In order to improve the heat-sealability at low-temperature of propylene resins to be used for sealant layers, various techniques have heretofore been developed for copolymerizing propylene with other olefin(s) such as ethylene or xcex1-olefins. However, most conventional techniques require copolymerization of propylene with a large amount of olefin(s) in order to make the resulting copolymers have good heat-sealability at low-temperature, resulting in that copolymers formed contain a large amount of unfavorable sticky side products which greatly lower the anti-blocking property of the copolymers. To solve this problem, known is a method of removing the sticky components by dissolving them in inert solvents. However, this method is still problematic in that the low-temperature-melting crystalline components that exist in the copolymers and are indispensable for the heat-sealability at low-temperature of the copolymers are also dissolved out of the copolymers, thus causing a condition in that the heat-sealability at low-temperature of the copolymers is worsened.
On the other hand, since the resins used for such heat-sealing layers are expensive, recently used are multi-laminate films having thinner heat-sealing layers that is surface layers and therefor having higher stiffness as a whole. In such multi-laminate films, a low-temperature heat-sealing property of them depends on not only resin characteristics of heat-sealing layers but also on that of substrate layers. Therefore, the resin characteristics of substrate layers also have been tried to be improved. For example, one attempt is to copolymerize propylene with ethylene, 1-butene or the like comonomer to give resin substrate layers, which, however, is still problematic in that the copolymerization greatly lowers the crystallinity of the resins formed and therefore the resins could not have good stiffness.
In addition to their good heat-sealability at low-temperature and high strength after heat sealing, films are further required to have good slipping and anti-blocking properties in the step of re-winding the films being produced, and also to have good outward appearance and good transparency. Moreover, desired are resins capable of being formed into high-quality films even in recent high-producible, large-scale sheeting machines and high-speed sheeting machines.
On the other hand, in general, wrapping films are formed into bags through heat sealing; then the bags are charged with contents and closed also through heat sealing, and thereafter final consumers open the sealed bags to take out the contents. Thus, the process from the sheeting of those wrapping films to the end of their role takes a long time. Therefore, wrapping films are required to maintain their good quality, especially impact resistance, for the necessary period of time and under ordinary temperature conditions. Unfortunately, however, no example is known at least at present capable of satisfactorily removing the unfavorable phenomena of wrapping films, such as the reduction in their impact resistance and the reduction in their transparency.
One object of the invention is to provide a propylenic random copolymer capable of being sheeted into films having good heat-sealability at low-temperature and good slipping and anti-blocking properties necessary for high-speed sheeting of the copolymer without interfering with the intrinsic good characteristics of polypropylene films.
Another object of the invention is to provide a multi-layered film capable of exhibiting extremely high stiffness and good heat-sealability at low-temperature that are well balanced to each other, without interfering as much as possible with the intrinsic good characteristics of polypropylene films.
We, the present inventors have assiduously studied in order to attain the above-mentioned objects of the invention and, as a result, have found that, when a propylenic copolymer (A) or (B) having the specific characteristics mentioned below and containing a reduced amount of sticky components is sheeted into films, the resulting films have good slipping and anti-blocking properties and have extremely excellent heat-sealability at low-temperature.
In addition, the inventors have further found that a multi-layered laminate film comprising a substrate layer of a propylenic random copolymer (C) having the specific characteristics mentioned below, and a surface layer of the propylenic copolymer (A) or (B) having the specific characteristics mentioned below, as formed at least on one surface of the substrate layer has extremely high stiffness and good heat-sealability at low-temperature that are well balanced to each other. On the basis of these findings, we have completed the present invention.
Specifically, the invention provides a propylenic copolymer and its film, and also a multi-layered laminate film comprising the copolymer film, which are as follows:
[1] A propylenic copolymer (A) of propylene and ethylene, which satisfies the following (1) to (3):
(1) The ethylene unit content (xa, wt. %) of the copolymer is from 3 to 10 wt. %.
(2) The relation between the boiling diethyl ether extraction (Ea, wt. %) of the copolymer and xa satisfies the following (I) or (II):
Eaxe2x89xa60.25xa+1.1(xa=3 to 6 wt. %)xe2x80x83xe2x80x83(I) 
Eaxe2x89xa62.6(xa=6 to 10 wt. %)xe2x80x83xe2x80x83(II) 
(3) The relation between the melting point (Tm, xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xa satisfies the following (III) or (IV):
Tmaxe2x89xa6140(xa=3 to 5 wt. %)xe2x80x83xe2x80x83(III) 
Tmaxe2x89xa6165xe2x88x925xa(xa=5 to 10 wt. %)xe2x80x83xe2x80x83(IV) 
[2] The propylene-ethylene copolymer (A) of [1], which further satisfies the following (4) and (5):
(4) The copolymer has a melt index (MIa, g/10 min) of from 4 to 12 g/10 min.
(5) The isotactic triad fraction (mma, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 98.0 mol %.
[3] A film as formed by sheeting the propylenic random copolymer (A) of any one of [1] or [2].
[4] A film of a copolymer of propylene and ethylene, which satisfies the following (6) to (8):
(6) The ethylene unit content (xf, wt. %) of the copolymer composing the film is from 3 to 10 wt. %.
(7) The relation between the heat of fusion of the film as measured with a differential scanning calorimeter at 120xc2x0 C. or lower (xcex94H120, J/g) and xf satisfies the following (V) or (VI):
xcex94H120xe2x89xa714(xf=3 to 5 wt. %)xe2x80x83xe2x80x83(V) 
xcex94H120xe2x89xa75xfxe2x88x9211(xf=5 to 10 wt. %)xe2x80x83xe2x80x83(VI) 
(8) The isotactic triad fraction (mmf, mol %) in the PPP sequence of the copolymer composing the film, as measured in 13C-NMR, is not smaller than 98.0 mol %.
The invention further provides the following propylenic random copolymer and its film.
[5] A propylenic random copolymer (B) of propylene and ethylene, which satisfies the following (9) to (11):
(9) The ethylene unit content (xb, wt. %) of the copolymer is from 0.2 to 15 wt. %.
(10) The relation between the boiling diethyl ether extraction (Eb, wt. %) of the copolymer and xb satisfies the following (1) or (2):
Ebxe2x89xa60.2xb+1.0(0.2xe2x89xa6xb  less than 5)xe2x80x83xe2x80x83(1) 
Ebxe2x89xa62.0(5xe2x89xa6xbxe2x89xa615)xe2x80x83xe2x80x83(2) 
(11) The relation between the melting point (Tmb, xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xb satisfies the following (3) or (4):
Tmbxe2x89xa6140(0.2xe2x89xa6xb less than 4)xe2x80x83xe2x80x83(3) 
Tmbxe2x89xa6160xe2x88x925xb(4xe2x89xa6xbxe2x89xa615)xe2x80x83xe2x80x83(4) 
[6] The propylene-ethylene random copolymer (B), which further satisfies the following (12) to (14):
(12) The copolymer has a melt index (MIb, g/10 min) of from 0.1 to 15 g/10 min.
(13) The isotactic triad fraction (mmb, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 90 mol %.
(14) The relation between the PEP sequence content (R, mol %) of the copolymer as measured in 13C-NMR, and xb satisfies the following (5):
Rxe2x89xa70.5xb+1.0xe2x80x83xe2x80x83(5) 
[7] A film as formed by sheeting the propylenic random copolymer of any one of [5] or [6].
The invention still further provides a multi-layered film as formed through lamination of specific propylenic random copolymers.
[8] A multi-layered film of propylenic random copolymers, which comprises a surface layer of the following propylenic copolymer (A) as formed on at least one surface of a substrate layer of the following propylenic random copolymer (C):
Propylenic random copolymer (C) satisfying the following (15) to (17):
(15) The ethylene unit content (xc, wt. %) of the copolymer is from 0.2 to 4 wt. %.
(16) The relation between the boiling diethyl ether extraction (Ec, wt. %) of the copolymer and xc satisfies the following (XII):
Ecxe2x89xa60.25xc+1.1xe2x80x83xe2x80x83(XII) 
(17) The relation between the melting point (Tmc, xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xc satisfies the following (XIII):
Tmcxe2x89xa6165xe2x88x925xcxe2x80x83xe2x80x83(XIII) 
Propylenic random copolymer (A) satisfying the following (1) to (3):
(1) The ethylene unit content (xa, wt. %) of the copolymer is from 3 to 10 wt. %.
(2) The relation between the boiling diethyl ether extraction (Ea, wt. %) of the copolymer and xa satisfies the following (I) or (II):
Eaxe2x89xa60.25xa+1.1(xa=3 to 6 wt. %)xe2x80x83xe2x80x83(I) 
Eaxe2x89xa62.6(xa=6 to 10 wt. %)xe2x80x83xe2x80x83(II) 
(3) The relation between the melting point (Tma, xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xa satisfies the following (III) or (IV):
Tmaxe2x89xa6140(xa=3 to 5 wt. %)xe2x80x83xe2x80x83(III) 
Tmaxe2x89xa6165xe2x88x925xa(xa=5 to 10 wt. %)xe2x80x83xe2x80x83(IV) 
[9] The multi-layered film of propylenic random copolymers of [8], in which the surface layer of the propylenic random copolymer (A) further satisfies the following (4) and (5):
(4) The copolymer has a melt index (MIa, g/10 min) of from 4 to 12 g/10 min.
(5) The isotactic triad fraction (mma, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 98.0 mol %.
[10] The multi-layered film of propylenic random copolymers of [8], in which the substrate layer of the propylenic random copolymer (C) further satisfies the following (18) and (19):
(18) The copolymer has a melt index (MIc, g/10 min) of from 4 to 12 g/10 min.
(19) The isotactic triad fraction (mmc, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 98 mol %.
[11] The multi-layered film of propylenic random copolymers of [9], in which the substrate layer of the propylenic random copolymer (C) further satisfies the following (18) and (19):
(18) The copolymer has a melt index (MIc, g/10 min) of from 4 to 12 g/10 min.
(19) The isotactic triad fraction (mmc, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 98 mol %.
[12] A multi-layered film of propylenic random copolymers, which comprises a surface layer of the following propylenic copolymer (B) as formed on at least one surface of a substrate layer of the following propylenic random copolymer (C):
Propylenic random copolymer (C) satisfying the following (15) to (17):
(15) The ethylene unit content (xc, wt. %) of the copolymer is from 0.2 to 4 wt. %.
(16) The relation between the boiling diethyl ether extraction (Ec, wt. %) of the copolymer and xc satisfies the following (XII):
Ecxe2x89xa60.25xc+1.1xe2x80x83xe2x80x83(XII) 
(17) The relation between the melting point (Tmc, xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xc satisfies the following (XIII):
Tmcxe2x89xa6165xe2x88x925xcxe2x80x83xe2x80x83(XIII) 
Propylenic random copolymer (B) satisfying the following (9) to (11):
(9) The ethylene unit content (xb, wt. %) of the copolymer is from 0.2 to 15 wt. %.
(10) The relation between the boiling diethyl ether extraction (Eb, wt. %) of the copolymer and xb satisfies the following (VII) or (VIII):
Ebxe2x89xa60.2xb+1.0(0.2xe2x89xa6xb less than 5)xe2x80x83xe2x80x83(VII) 
Ebxe2x89xa62.0(5xe2x89xa6xbxe2x89xa615)xe2x80x83xe2x80x83(VIII) 
(11) The relation between the melting point (Tmb, xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xb satisfies the following (IX) or (X):
Tmbxe2x89xa6140(0.2xe2x89xa6xbxe2x89xa64)xe2x80x83xe2x80x83(IX) 
Tmbxe2x89xa6160xe2x88x925xb(4xe2x89xa6xbxe2x89xa615)xe2x80x83xe2x80x83(X) 
[13] The multi-layered film of propylenic random copolymers of [12], in which the surface layer of the propylenic random copolymer (B) further satisfies the following (12) to (14):
(12) The copolymer has a melt index (MIb, g/10 min) of from 0.1 to 15 g/10 min.
(13) The isotactic triad fraction (mmb, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 90 mol %.
(14) The relation between the PEP sequence content (R, mol %) of the copolymer as measured in 13C-NMR, and xb satisfies the following (XI):
Rxe2x89xa70.5xb+1.0xe2x80x83xe2x80x83(XI) 
[14] The multi-layered film of propylenic random copolymers of [12], in which the substrate layer of the propylenic random copolymer (C) further satisfies the following (18) and (19):
(18) The copolymer has a melt index (MIc, g/10 min) of from 4 to 12 g/10 min.
(19) The isotactic triad fraction (mmc, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 98 mol %.
[15] The multi-layered film of propylenic random copolymers of [13], in which the substrate layer of the propylenic random copolymer (C) further satisfies the following (18) and (19):
(18) The copolymer has a melt index (MIc, g/10 min) of from 4 to 12 g/10 min.
(19) The isotactic triad fraction (mmc, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 98 mol %.
[16] The multi-layered film of propylenic random copolymers of any one of [8] to [15], in which the thickness ratio of the surface layer to the substrate layer (surface layer/substrate layer) is between 0.005 and 0.5.
[17] The multi-layered film of propylenic random copolymers of any one of [8] to [15], in which the propylenic random copolymer (C) further satisfies the following (20):
(20) The relation between the melt index (MIc, g/10 min) of the copolymer and the time of relaxation (t, sec) of the copolymer as obtained through frequency dispersion measurement at a frequency xcfx890=100 rad/sec satisfies the following (XIV):
xcfx84xe2x89xa60.65xe2x88x920.025 MIcxe2x80x83xe2x80x83(XIV) 
Now, the invention is described in detail hereinunder.
The propylenic copolymer (A) of the invention is obtained through copolymerization of propylene and ethylene, and satisfies the following (1) to (3):
(1) The ethylene unit content (xa, wt. %) of the propylenic copolymer (A) is from 3 to 10 wt. %, preferably from 3.5 to 9 wt. %, more preferably from 4 to 9 wt. %. If xa is less than 3 wt. %, the heat-sealing temperature of the copolymer could not be lowered satisfactorily. If, however, it is more than 10 wt. %, the stiffness of the copolymer is lowered, and the copolymer shall contain a large amount of sticky components, resulting in that its anti-blocking property tends to be worsened.
(2) The relation between the boiling diethyl ether extraction (Ea, wt. %) of the copolymer and xa satisfies the following (I) or (II):
Eaxe2x89xa60.25xa+1.1(xa=3 to 6 wt. %)xe2x80x83xe2x80x83(I) 
Eaxe2x89xa62.6(xa=6 to 10 wt. %)xe2x80x83xe2x80x83(II) 
If E oversteps the defined range, the anti-blocking property of the copolymer is worsened, and in addition, the heat-sealing temperature of the copolymer could not be lowered satisfactorily.
In particular, the following relation is more preferred.
Eaxe2x89xa60.20xa+1.1(xa=3 to 6 wt. %)xe2x80x83xe2x80x83(Ixe2x80x2) 
Eaxe2x89xa62.3(xa=3 to 6 wt. %)xe2x80x83xe2x80x83(IIxe2x80x2) 
(3) The relation between the melting point (Tma, xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xa satisfies the following (III) or (IV):
Tmaxe2x89xa6140(xa=3 to 5 wt. %)xe2x80x83xe2x80x83(III) 
Tmaxe2x89xa6165xe2x88x925xa(xa=5 to 10 wt. %)xe2x80x83xe2x80x83(IV) 
If Tma oversteps the defined range, the heat-sealing temperature of the copolymer could not be lowered satisfactorily.
In particular, the following relation is more preferred.
xe2x80x83Tmaxe2x89xa6140(xa=3 to 4 wt. %)xe2x80x83xe2x80x83(IIIxe2x80x2)
Tmaxe2x89xa6160xe2x88x925xa(xa=4 to 10 wt. %)xe2x80x83xe2x80x83(IVxe2x80x2) 
Preferably, the propylenic copolymer (A) of the invention further satisfies the following (4) and/or (5):
(4) The propylenic copolymer (A) has a melt index (MIa, g/10 min) of preferably from 4 to 12 g/10 min, more preferably from 5 to 10 g/10 min. If its MIa is lower than 4 g/10 min, the transparency and impact resistance of the film of the copolymer will often be poor. If, however, its MIa is higher than 12 g/10 min, the copolymer will often be sheeted into failed films.
(5) The isotactic triad fraction (mma, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is preferably not smaller than 98.0 mol %, more preferably not smaller than 98.5 mol %
If mma is smaller than 98.0 mol %, the copolymer contains a large amount of sticky components, resulting in that its anti-blocking property tends to be worsened. If so, in addition, the crystallinity of the copolymer is lowered so that its stiffness is lowered. Moreover, the melting point depression in the copolymer relative to the comonomer amount is small, resulting in that the heat-sealing temperature of the copolymer could not often be lowered satisfactorily.
The film of the propylenic copolymer (A) has good heat-sealability, high stiffness, good anti-blocking and slipping properties, and high transparency. In addition, even when the copolymer (A) is sheeted at a high sheeting speed, the quality of the film formed is lowered little.
The propylene-ethylene copolymer film of the invention which satisfies the following (6) to (8) has good heat-sealability, high stiffness, good anti-blocking and slipping properties, and high transparency. In addition, even when the copolymer is sheeted at a high sheeting speed, the quality of the film formed is lowered little. The film is suitably used as a sealant layer of laminate films.
(6) The comonomer unit content (xf, wt. %) of the copolymer composing the film is from 3 to 10 wt. %, preferably from 4 to 9 wt. %. If xf is smaller than 3 wt. %, the heat-sealing temperature of the film could not often be lowered satisfactorily. However, if xf is larger than 10 wt. %, the stiffness and the anti-blocking property of the film will be often lowered.
(7) The relation between the heat of fusion of the film as measured with a differential scanning calorimeter at 120xc2x0 C. or lower (xcex94H120, J/g) and xf satisfies the following (V) or (VI):
xcex94H120xe2x89xa714(xf=3 to 5 wt. %)xe2x80x83xe2x80x83(V) 
xcex94H120xe2x89xa75xfxe2x88x9211(xf=5 to 10 wt. %)xe2x80x83xe2x80x83(VI) 
If xcex94H120 is lower than the defined range, the heat-sealing temperature of the film could not often be lowered satisfactorily.
In particular, preferred is the following relation:
xcex94H120xe2x89xa714(xf=3 to 5 wt. %)xe2x80x83xe2x80x83(Vxe2x80x2) 
xcex94H120xe2x89xa78xfxe2x88x9226(xf=5 to 10 wt. %)xe2x80x83xe2x80x83(VIxe2x80x2) 
(8) The isotactic triad fraction (mmf, mol %) in the PPP sequence of the copolymer composing the film, as measured in 13C-NMR, is not smaller than 98.0 mol %, preferably not smaller than 98.5 mol %.
If mmf is smaller than 98.0 mol %, the film shall contain a large amount of sticky components, resulting in that its anti-blocking property will be lowered, and the crystallinity of the copolymer composing the film is lowered, meaning that the stiffness of the film will be often low. If so, in addition, the melting point depression in the film relative to the comonomer amount is small, resulting in that the heat-sealing temperature of the film could not often be lowered satisfactorily.
The propylenic random copolymer (B) of the invention is obtained through random copolymerization of propylene and ethylene, and satisfies the following (9) to (11):
(9) The ethylene unit content (xb, wt. %) of the propylenic random copolymer is from 0.2 to 15 wt. %, preferably from 3 to 10 wt. %. If xb is less than 0.2 wt. %, the heat-sealing temperature of the copolymer could not be lowered satisfactorily, and in addition, the crystallinity of the copolymer is too high. Therefore, if the copolymer is sheeted at a high sheeting speed, the resulting film will often have poor impact resistance. If, however, xb is more than 15 wt. %, the stiffness of the copolymer is lowered, and the copolymer shall contain a large amount of sticky components, resulting in that its anti-blocking property is worsened.
(10) The relation between the boiling diethyl ether extraction (Eb, wt. %) of the copolymer and xb satisfies the following (VII) or (VIII):
Ebxe2x89xa60.2xb+1.0(0.2xe2x89xa6xbxe2x89xa65)xe2x80x83xe2x80x83(VII) 
Ebxe2x89xa62.0(5xe2x89xa6xbxe2x89xa615)xe2x80x83xe2x80x83(VIII) 
If Eb oversteps the defined range, the anti-blocking property of the copolymer is worsened, and in addition, the heat-sealing temperature of the copolymer could not be lowered satisfactorily.
In particular, the following relation is more preferred.
Ebxe2x89xa60.2xb+0.5(0.2xe2x89xa6xbxe2x89xa65)xe2x80x83xe2x80x83(VIIxe2x80x2) 
Ebxe2x89xa61.5(5xe2x89xa6xbxe2x89xa615)xe2x80x83xe2x80x83(VIIIxe2x80x2) 
(11) The relation between the melting point (Tmb xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xb satisfies the following (IX) or (X):
xe2x80x83Tmbxe2x89xa6140(0.2xe2x89xa6xbxe2x89xa64)xe2x80x83xe2x80x83(IX)
Tmbxe2x89xa6160xe2x88x925xb(4xe2x89xa6xbxe2x89xa615)xe2x80x83xe2x80x83(X) 
If Tmb oversteps the defined range, the heat-sealing temperature of the copolymer could not be lowered satisfactorily.
In particular, the following relation is more preferred.
Tmbxe2x89xa6155xe2x88x925xb(0.2xe2x89xa6xbxe2x89xa615)xe2x80x83xe2x80x83(Xxe2x80x2) 
Preferably, the propylenic copolymer (B) of the invention further satisfies at least one of the following (12) to (14):
(12) The propylenic random copolymer has a melt index (MIb, g/10 min) of preferably from 0.1 to 15 g/10 min, more preferably from 1 to 2 g/10 min. If its MIb is lower than 0.1 g/10 min, the transparency and impact resistance of the film of the copolymer tends to be poor. If, however, its MI is higher than 15 g/10 min, the copolymer will often be sheeted into failed films.
(13) The isotactic triad fraction (mmb, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is preferably not smaller than 90 mol %, more preferably not smaller than 94 mol %
If mmb is smaller than 90 mol %, the copolymer contains a large amount of sticky components, resulting in that its anti-blocking property tends to be worsened. If so, in addition, the crystallinity of the copolymer is lowered so that its stiffness is lowered. Moreover, the melting point depression in the copolymer relative to the comonomer amount is small, resulting in that the heat-sealing temperature of the copolymer could not often be lowered satisfactorily.
(14) The relation between the PEP sequence content (R, mol %) of the copolymer as measured in 13C-NMR, and xb preferably satisfies the following (XI):
Rxe2x89xa705xb+1.0xe2x80x83xe2x80x83(XI) 
If R is smaller than the defined range, the melting point depression in the copolymer relative to the comonomer amount is small, resulting in that the heat-sealing temperature of the copolymer could not often be lowered satisfactorily. In addition, if so, the copolymer contains a large amount of sticky components, resulting in that its anti-blocking property tends to be worsened.
In particular, more preferred is the relation satisfying the following:
Rxe2x89xa70.5xb+2.0xe2x80x83xe2x80x83(XIxe2x80x2) 
The propylenic random copolymer can be sheeted into films having good heat-sealability at low-temperature and especially having good slipping and anti-blocking properties which are necessary for working the films at a high working speed, without interfering with as much as possible the intrinsic good characteristics of polypropylene films. In addition, the films of the copolymer have high transparency and good impact resistance. Even when the copolymer is sheeted at a high sheeting speed, the quality of the resulting films decreases but little.
The propylenic random copolymer (A) and (B) of the invention can be separately formed into corresponding film having especially good heat-sealability at low-temperature. The resulting single-layered film, and even multi-layered film comprising the film of the propylenic random copolymer (A) or (B) of the invention and single-layered or multi-layered film of other resins can be used favorably for wrapping use and in other various applications. The other resins include, for example, polyolefin resins such as polypropylene resins, as well as polyester resins, ethylene-vinyl acetate copolymers (EVA), etc.
The above multi-layered films can be produced by separately preparing the substrate layer and the surface layer followed by laminating them in a known dry-laminating method, or can be produced at a time by co-extruding the each layers in a known co-extruding method.
In such a multi-layered film, it is especially advantageous that a sealant surface layer of the copolymer of the invention is laminated or co-extruded on at least one surface of the substrate layer of other resins to give multi-layered films.
Other embodiments of the multi-layered film comprising the propylenic random copolymer of the invention are mentioned hereinunder.
The invention includes multi-layered films with high heat-sealing strength, which have maintained high stiffness and increased low-temperature heat-sealing property and can be thinned to meet the recent requirements for thin films. Specifically, the invention provides a multi-layered film comprising a substrate layer of a film of a specific propylenic random copolymer (C) and a surface layer of a film of the propylenic random copolymer (A) or (B) as formed on at least one surface of the substrate layer.
The propylenic random copolymer (C) to form the substrate layer constituting the multi-layered film of the invention shall satisfy the following (15) to (17):
(15) The ethylene unit content (xc, wt. %) of the copolymer is from 0.2 to 4 wt. %, preferably from 0.5 to 3.5 wt. %. If xc is less than 0.2 wt. %, the meltability at low-temperature of the substrate layer of the copolymer is poor. In particular, where a thin surface layer is formed on the substrate layer, the heat-sealability at low-temperature of the substrate layer is especially poor. In addition, if so, the crystallinity of the copolymer is too high, resulting in that the transparency and impact strength of multi-layered film to be formed from the copolymer will be poor when the film is formed at a high sheeting speed. On the other hand, if xc is more than 4 wt. %, the stiffness of the substrate layer of the copolymer tend to be low, resulting in that the anti-blocking property of the surface layer to be formed thereon is also lowered.
(16) The relation between the boiling diethyl ether extraction (Ec, wt. %) of the copolymer and xc satisfies the following (XII):
Ecxe2x89xa60.25xc+1.1xe2x80x83xe2x80x83(XII) 
If Ec oversteps the defined range, the anti-blocking property of the surface layer of the copolymer (A) to be formed over the substrate layer is poor.
Preferably;
Ec0.2xc+1.1xe2x80x83xe2x80x83(XIIxe2x80x2). 
(17) The relation between the melting point (Tmc, xc2x0 C.) of the copolymer as measured with a differential scanning calorimeter and xc satisfies the following (XIII):
Tmcxe2x89xa6165xe2x88x925xc(XIII) 
If Tmc oversteps the defined range, the meltability at low-temperature of the substrate layer of the copolymer is poor. Therefore, if a thin surface layer is formed over the substrate layer, the heat-sealability at low-temperature of the resulting laminate film or co-extruded film is poor.
Preferably;
Tmcxe2x89xa6162xe2x88x925xc(XIIIxe2x80x2). 
Preferably, the propylenic random copolymer (C) to form the substrate layer constituting the multi-layered film of the invention additionally satisfies at least one of the following (18) to (20):
(18) The copolymer has a melt index (MIc, g/10 min) of from 4 to 12 g/10 min, preferably from 5 to 10 g/10 min.
If MIc is lower than 4 g/10 min, the transparency and the impact resistance of the layer of the copolymer will often be poor. However, if it is higher than 12 g/10 min, the copolymer will often be sheeted into failed films.
(19) The isotactic triad fraction (mmc, mol %) in the PPP sequence of the copolymer, as measured in 13C-NMR, is not smaller than 98 mol %, preferably not smaller than 98.5 mol %.
If mmc is smaller than 98 mol %, the copolymer shall contain a large amount of sticky components, resulting in that its anti-blocking property tend to be poor. In addition, since the crystallinity of the copolymer tend to be lowered, often resulting in that its stiffness is lowered. Moreover, since the melting point depression in the copolymer relative to the comonomer amount is small, often resulting in that the melting point of the layer of the copolymer could not be lowered satisfactorily.
(20) The relation between the melt index (MIc, g/l0 min) of the copolymer and the time of relaxation (xcfx84, sec) of the copolymer as obtained through frequency dispersion measurement at a frequency xcfx890=100 rad/sec satisfies the following (XIV):
xe2x89xa60.65xe2x88x920.025 MIcxe2x80x83xe2x80x83(XIV) 
If xcfx84 oversteps the defined range, the transparency and impact resistance of the layer of the copolymer will often be poor when the copolymer is sheeted into the layer at a high sheeting speed.
In particular, more preferred is the relation satisfying the following:
xcfx84xe2x89xa60.63xe2x88x920.025 MIcxe2x80x83xe2x80x83(XIVxe2x80x2) 
On the other hand, the surface layer of the multi-layered film is sheeted from the propylenic random copolymer (A) or (B). The propylenic random copolymer (A) or (B) satisfies the requirements (1) to (3), or the requirements (6) to (8), and preferably further satisfies the requirements (4) and (5), or the requirements (9) to (11). The propylenic random copolymer (C) is preferably different from the propylenic random copolymer (A) or (B).
Preferably, the multi-layered film of those propylenic random copolymers of the invention is such that the thickness ratio of the surface layer of the propylene-ethylene random copolymer (A) or (B) to the substrate layer of the propylenic random copolymer (C) (surface layer/substrate layer) falls between 0.005 and 0.5, more preferably between 0.01 and 0.2.
If the ratio is larger than 0.5, the stiffness of the multi-layered film will often be poor. If, however, the ratio is smaller than 0.005, the multi-layered film tend to be difficult to shape and, in addition, the multi-layered film could not often exhibit satisfactorily the heat-sealability at low-temperature of the sealant surface layer of the multi-layered film.
The propylenic copolymers (A), (B) and (C) can be produced under specific polymerization conditions in the presence of specific catalysts, for example, in the manner mentioned hereinunder. However, such specific conditions and specific catalysts are not limitative.
The catalysts usable in producing the propylenic copolymers (A), (B) and (C) comprise, for example, (a) a solid catalyst component (a) consisting essentially of magnesium, titanium and a halogen, (b) a catalyst component of an organic metal compound such as an organic aluminium compound, and (c) a catalyst component of an electron donor compound such as an organic silicon compound. Concretely, the following catalyst components are employable herein.
Preferred carriers for the solid catalyst component can be obtained by reacting a metal magnesium, an alcohol, and a halogen and/or a halogen-containing compound.
The metal magnesium may be in any form of granular, ribbon-like, or powdery ones. Preferably, the metal magnesium is not coated with any substance other than metal magnesium, such as magnesium oxide.
The alcohol is preferably a lower alcohol having from 1 to 6 carbon atoms, such as methanol or ethanol. Especially preferred is ethanol, as easily giving good catalysts having high activity.
The halogen is preferably chlorine, bromine or iodine. Of those, especially preferred is iodine. As the halogen-containing compound, preferably used is MgCl2 or MgI2.
The amount of the alcohol to be used is preferably from 2 to 100 mols, more preferably from 5 to 50 mols, per mol of the metal magnesium.
The amount of the halogen or halogen-containing compound to be used may be generally 0.0001 gram-atoms or more, preferably from 0.0005 to 0.1 gram-atoms, especially preferably from 0.001 to 0.06 gram-atoms or more, in terms of the amount of the halogen atom itself or of the amount of the halogen atom in the halogen-containing compound, relative to 1 gram-atom of the metal magnesium. One or more halogens or halogen-containing compounds can be used either singly or as combined.
The carrier of the catalyst for use in the invention can be obtained generally by reacting the metal magnesium, alcohol, and halogen and/or halogen-containing compound, for example, under reflux (at about 79xc2x0 C.) until hydrogen gas is no more formed, generally for from 20 to 30 hours. This reaction is preferably effected in an inert gas atmosphere such as nitrogen gas or argon gas.
The thus-obtained carrier is filtered out and dried, optionally after having been washed with an inert solvent such as heptane, and is used in producing the solid catalyst component (a).
Preferably, the carrier is nearly granular, while having a narrow grain size distribution to give a sharp peak. More preferably, the variation in the shape of each grain constituting the carrier is as small as possible. Concretely, the sphericity (S) of each grain to be represented by the following (XV) is preferably less than 1.60, more preferably less than 1.40, and the grain size distribution index (P) to be represented by the following (XVI) is preferably less than 5.0, more preferably less than 4.0.
S=(E1/E1)2xe2x80x83xe2x80x83(XV) 
wherein E1 indicates the length of the projected border line of each grain; and E2 indicates the circumference of the circle of which the area is the same as the projected area of each grain.
P=D90/D10xe2x80x83xe2x80x83(XVI) 
wherein D90 indicates a grain size corresponding to the weight cumulative fraction of 90%. In other words, D90 means that the weight sum of the grains having a grain size smaller than the grain size represented by D90 is 90% of the total weight sum of all grains. The same shall apply also to D10.
The solid catalyst component is produced by contacting the carrier with at least a titanium compound.
The titanium compound may be one represented by a general formula (XVII):
TiX1n(OR1)4xe2x88x92nxe2x80x83xe2x80x83(XVII) 
wherein X1 represents a halogen atom, especially preferably a chlorine atom; R1 represents a hydrocarbon group having from 1 to 10 carbon atoms, especially preferably a linear or branched alkyl group, and plural R1""s, if any, may be the same or different; and n is an integer of from 0 to 4.
Concretely, the titanium compound includes Ti(O-i-C3H7)4, Ti(Oxe2x80x94C4H9)4, TiCl(Oxe2x80x94C2H5)3, TiCl(O-i-C3H7)3, TiCl(Oxe2x80x94C4H9)3, TiCl2(Oxe2x80x94C4H9)2, TiCl2(O-i-C3H7)2, TiCl4. Of those, especially preferred is TiCl4.
Generally, the solid catalyst component is produced by further contacting the carrier with an electron donor compound.
The electron donor compound is preferably an aromatic dicarboxylate, especially preferably di-n-butyl phthalate and di-ethyl phthalate.
While the carrier is contacted with the titanium compound and the electron donor compound, in general, it is further contacted with a halogen-containing silicon compound. The halogen-containing silicon compound is preferably silicon tetrachloride.
The solid catalyst compound can be produced in any known manner. For example, the carrier is added to a solvent along with an electron donor compound and a halogen-containing silicon compound such as those mentioned above, then a titanium compound such as that mentioned above is added thereto with stirring, and all those are reacted. The solvent is preferably an inert hydrocarbon such as pentane, hexane, heptane or octene. The electron donor compound is used generally in an amount of from 0.01 to 10 mols, preferably from 0.5 to 5 mols, per mol of the carrier in terms of the magnesium atom; and the titanium compound is used generally in an amount of from 1 to 50 mols, preferably from 2 to 20 mols, per mol of the carrier in terms of the magnesium atom. The reaction is effected by contacting the components with each other, generally at a temperature falling between 0 and 200xc2x0 C. for from 5 minutes to 10 hours, preferably between 30 and 150xc2x0 C. for from 30 minutes to 5 hours.
After the reaction, it is preferred that the solid catalyst component formed is washed with an inert hydrocarbon (e.g., n-hexane, n-heptane).
Of the catalyst components, the organic metal compound is preferably an organic aluminium compound.
For this, widely used are organic aluminium compounds of the following general formula (XVIII):
AlR2nX23xe2x88x92nxe2x80x83xe2x80x83(XVIII) 
wherein R2 represents an alkyl group having from 1 to 10 carbon atoms, a cycloalkyl group, or an aryl group; X2 represents a halogen atom and is preferably a chlorine or bromine atom; and n is an integer of from 1 to 3.
Concretely, the compounds include trialkyl aluminium compounds such as trimethyl aluminium, triethyl aluminium, triisobutyl aluminium; and also diethylaluminium monochloride, diisobutylaluminium monochloride, diethylaluminium monoethoxide, ethylaluminium sesquichloride, etc. Of those, preferred are triethyl aluminium and triisobutyl aluminium. One or more of those compounds can be used either singly or as combined.
Of the catalyst components, the electron donor compound to act on the polymerization system is preferably an organic silicon compound. Especially preferred are dicyclopentyldimethoxysilane and cyclohexylmethyldimethoxysilane.
The solid catalyst component is used in the intended polymerization, preferably after having been pre-treated. To pre-treat it, preferably, it is reacted with a small amount of propylene introduced, under the condition of the existence of the solid catalyst component, organic metal compound and an electron donor compound such as those mentioned hereinabove with stirring them. Where the solid catalyst component and so on are put into the reactor, it is preferable that those components are solved in a proper solvent before being put in to avoid the solid catalyst component from adhering to the inner wall of the reactor. The solvent is preferably discharged from the reactor at the latest up to the initial stage of the reaction. Such a solvent is preferably an inert hydrocarbon such as pentane, hexane, heptane, octene or the like. The organic metal compound is used in an amount of generally from 0.01 to 10 mols, preferably from 0.05 to 5 mols, per mol of the titanium atom in the solid catalyst component; and the electron donor compound is used in an amount of generally from 0.01 to 20 mols, preferably from 0.1 to 5 mols, per mol of the titanium atom in the solid catalyst. Propylene is added to the catalyst system at a propylene partial pressure higher than an atmospheric pressure, with which the solid catalyst is pre-treated preferably at from 0 to 100xc2x0 C. for from 0.1 to 24 hours. After the reaction, preferably, the pre-treated catalyst is washed with an inert hydrocarbon such as n-hexane or n-heptane.
The propylenic random copolymer of the invention is produced, for example, by feeding predetermined amounts of propylene and ethylene under the existence of the solid catalyst component, the organic metal compound and the electron donor compound all mentioned above and reacting with stirring. The solid catalyst component used in the intended polymerization is preferably put into a reactor after solving them to a proper solvent such as the above-mentioned inert hydrocarbon to avoid the solid catalyst component from adhering to the inner wall of the reactor. The solvent is preferably discharged from the reactor at latest up to the initial stage of the reaction. The polymerization generally takes place under the condition that, for example, the monomers are copolymerized generally at a propylene partial pressure not lower than an atmospheric pressure, preferably between atmospheric pressure and 40 kg/cm2, and at a temperature falling between xe2x88x9280 and 150xc2x0 C., preferably between 20 and 150xc2x0 C. The organic metal compound is used generally in an amount of from 0.1 to 400 mols, preferably from 1 to 200 mols, per mol of the titanium atom in the solid catalyst component; and the electron donor compound is used generally in an amount of from 0.1 to 100 mols, preferably from 1 to 50 mols, per mol of the titanium atom in the solid catalyst.
The ethylene content of the propylenic random copolymers (A), (B) and (C) shall be changed by controlling the ethylene partial pressure and the amount of ethylene to be fed into the polymerization system; and the molecular weight of those copolymers shall be changed by controlling the amount of hydrogen to be introduced into the polymerization system.
The propylenic random copolymer (B) of the invention is obtained only when the copolymer powder obtained in accordance with the above-mentioned method is further washed with an organic solvent, which, however, is not limitative. Any other methods capable of giving the propylenic random copolymer (B) are employable. The ethylene content of the propylenic random copolymer (B) will slightly vary, depending on the condition for washing it with an organic solvent.
The organic solvent to be used for washing the propylenic random copolymer may be an inert solvent, such as heptane, hexane, cyclohexane or the like. Of those, preferred is heptane. The washing temperature varies, depending on the inert solvent used, but may be generally between 0 and 80xc2x0 C., preferably between 10 and 50xc2x0 C. For example, when heptane is used as the solvent, the copolymer may be washed at a temperature of 25+/xe2x88x925xc2x0 C. The washing may be repeated several times.
The propylenic copolymer, after having been produced in the manner mentioned hereinabove, is characterized in that its PPP sequence has a high degree of stereospecificity and can be highly randomly copolymerized with ethylene. After having been thus highly randomly copolymerized, the resulting propylenic random copolymer has high crystallinity while having a low melting point. In addition, since the degree of copolymerization of the polymer with ethylene is high, the melting point of the resulting copolymer can be effectively lowered even though the comonomer amount in the copolymer is small. Moreover, the compositional distribution of the random copolymer thus formed is narrow, and the copolymer contains a reduced amount of sticky components that cause the blocking of films of the copolymer. The sticky components in the copolymer are measured in terms of the boiling diethyl ether-soluble content of the copolymer.
The propylenic random copolymers (A), (B) and (C) of the invention can contain, if desired, any ordinary additives such as antioxidants, neutralizing agents, slipping aids, anti-blocking aids, and antistatic agents.
The propylenic random copolymers (A), (B) and (C) of the invention can be sheeted into films through T-die casting or melt extrusion. For those copolymers, preferred is a T-die casting method of sheeting the copolymer into films with a large-scale sheeting machine at a high sheeting speed. In such a T-die casting method, the copolymer can be sheeted into good films having a thickness of from 10 to 500 xcexcm even under a high-speed sheeting condition, for example, at a film taking-up speed of 50 m/min or higher.